This invention relates to improvements in a method of interpolating intervals in a measuring system.
"Interpolation" of an interval, such as a path interval, as used herein, means the subdivision of a signal period defined by the grid constant, or grid separation, of a grid measuring scale into a plurality of periods or subintervals. According to U.S. Pat. No. 4,225,931, the interpolation of an interval can be accomplished by converting at least one analog signal generated by a scanning unit which scans the scale into digital form by a converter, and feeding the digital signals into a digital computer for the automatic calculation therefrom of interpolation values within the signal period. The digital computer also receives as inputs the count of an up-down counter, and a binary control signal. The computer R is programmed to combine the values of the full signal period provided by the counter Z and the computed interpolation values to generate an interpolated position value. A display unit indicates the relative position of the scale and scanning unit in numerical form.
In the case of a high subdivision factor, for the evaluation of phase-shifted analog signals, it is necessary to optimize the signals for parameters of symmetry (involving the elimination of the signal direct-voltage component), amplitude equality, and required phase difference between signals.
For this purpose, U.S. Pat. No. 4,225,931 teaches the correction of the input digital signals for these parameters before the execution of the interpolation process. The correction is made by the computer according to correction values taken from a correction table which has previously been programmed into and stored in the computer. This method, however, requires the predetermination of the correction values, and the programming thereof into the computer.